The present invention relates to a box blank holding device in a box-making machine, which device holds blanks while moving them to a predetermined position and, more specifically, to a device of this kind that is capable of securely holding box blanks, already folded by the machine, regardless of the thickness and the hardness or softness of the blanks.
Conventionally, a box blank holding device in a box-making machine has a pair of holding members projecting from a main body adapted to, for example, be moved toward and away from each other by a gear mechanism so that the blanks are released when the holding members are moved away from each other. A means for moving the holding members toward and away from each other is adapted to, for example, move the pair of holding members close to each other until they are positioned so as to be separated by a predetermined width in accordance with the thickness of the blanks to be held, which blanks which may arranged in a stack.
However, in an arrangement wherein the pair of holding members project from the main body, they present obstacles to the feeding of blanks that are already folded by the box-making machine to the stacking section of the machine, particularly when the holding members are adapted to hold opposite sides of the blanks. If the space between the pair of holding members is increased in order to overcome this inconvenience, however, the stroke of the holding members during their movement toward each other is correspondingly increased. Such an increase is not desirable from a practical point of view, because it leads to a reduction in the working efficiency. In addition, because such an increase requires an increase in the length of the main body, the blank stacking section becomes large, and hence the entire machine may become undesirably long and large.
Furthermore, in an arrangement wherein the pair of holding members are moved toward each other by a gear mechanism so as to be separated by a predetermined width, if, for instance, the total thickness of the stacks of folded blanks varies among the stacks, the result will be that a stack having a total thickness greater than the predetermined width will be held under a higher pressure, whereas a stack having a total thickness less than the predetermined width will be held with a low pressure. Thus there is a risk that the blanks in a stack may be damaged or that they may not be held securely. In order to avoid such a risk it is necessary to adjust the space between the holding members for each stack, thereby adding operational inconvenience.
To solve the above-described problems, the present inventor proposed in Japanese Utility Model Laid-Open No. 43024/1989, corresponding to the U.S. parent application No. 07/309,346, a box blank holding device in a box-making machine, which device is capable of securely holding box blanks regardless of the thickness and the hardness or softness of the box blanks. As illustrated in FIGS. 7 and 8 of this application, this proposed blank holding device comprises a main body 1, a driving rack 3 movable by a supply of air to and a discharge of air from a cylinder 2, a transmission shaft 6 rotatably supported by the main body 1 and having a pair of pinions 4 and 5, one of the pinions 4 and 5 being in meshing engagement with the driving rack 3, a pair of holding member-actuating racks 7 and 8 disposed on opposite sides of the other pinion 5 of the transmission shaft 6 in meshing engagement with that pinion, retracting and projecting guide plates 9 mounted on the holder main body 1, and a pair of holding members 10 and 11 pivotally mounted on the ends of the holding member actuating racks 7 and 8 in such a manner as to be retractable and projectable while facing each other and being guided by the guide plates 9.
The above proposal succeeded in solving the problems of the conventional arrangement, and was provided with a specific form of means for projecting and retracting the pair of holding members. Such means is arranged as shown in FIGS. 7 and 8. Rollers 12 are disposed on the rear sides of the pair of holding members 10 and 11, respectively, and springs 15 or resilient members such as leaf springs are held between the shafts 13 of the rotors 12 and the mounting shafts 14 of the holding members 10 and 11 associated with the holding-member actuating racks 7 and 8. The resilient forces of the springs 15 always urge the corresponding holding members 10 and 11 in a direction in which the holding members are retracted (in the directions opposite the arrows in FIG. 7). When the holding-member actuating racks 7 and 8 are moved toward the transmission shaft 6 (in the directions of the corresponding arrows) along the projecting-and-retracting guide plates 9, the respective rotors 12 are raised while moving along the guide plates 9 of L-shaped cross section, thereby causing the holding members 10 and 11 to project inwardly. In this arrangement, each time a stack of box blanks is inverted, the holding members 10 and 11 must be projected and retracted at high speeds. This arrangement may lead to new kinds of problems: for example, the springs may be damaged or broken due to elastic fatigue or similar problems, causing an imperfect operation and reducing the overall service life of the device.